The present invention relates to a flame-retardant composition, and more particularly to a flame-retardant composition having excellent processability, which provides a resin composition having good heat resistance and appearance of molded articles when mixed with a resin or the like.
In order to make flammable resins flame retardant, halogen compounds, antimony trioxide and the like have been incorporated therein. However, it has been pointed out that these flame-retardation methods are not desirable in terms of environmental protection, toxicity and the like, and there is a demand to improve the flame-retardation methods. Phosphorus-based flame-retardants have been studied as a substitute for halogen-containing and metal oxide flame retardants. A proposed mechanism of the flame-retardation suggests that a polyphosphoric acid phase formed on the surface of the resin and a carbonized phase resulting from the dehydration of the resin during combustion. It is believed that the polyphosphoric acid phase and/or the carbonized phase acts as films to cut off heat and oxygen to the resin. Consequently, for resins that are difficult to form a carbonized film by dehydration, the flame-retardation must rely on the film of the polyphosphoric acid phase. Thus, without a substantial carbonized film, more polyphosphoric acid must be added to the resin. When compounds with a high phosphorus atom concentration are used, a high flame-retardation effect can be expected by adding them in a small amount. Red phosphorus, phosphoric acid esters, condensed phosphoric acid esters and the like have conventionally been used as phosphorus-based flame-retardants. Red phosphorus has had problems such as mold corrosion because corrosive phosphoric acid is produced by hydrolysis. A large amount of phosphorous addition has been required for phosphoric acid esters and condensed phosphoric acid esters as they have a relatively low concentration of phosphorus. This has deteriorated mechanical properties, thermal properties and the like, and caused problems such as cost increases due because of the amount of phosphorous.
On the other hand, phosphazene compounds such as aryloxy phosphazenes, alkoxy phosphazenes, thiophosphazenes, halogenated phosphazenes and phosphazene polymers derived from these compounds have been studied for use as flame-retardants, lubricant, incombustible electrolytic solutions and carcinostatic agents. Particularly in recent years, phosphazene compounds have attracted attention because they have a high phosphorus content, as well as high heat resistance, hydrolysis resistance and flame retardancy. Several methods have proposed imparting flame-retardation to resins using phosphazene compounds.
For example, JP-B-3-73590 proposes a flame-retardant resin composition including a polyphenylene ether with the customary molecular weight, polystyrene and a phosphazene compound; JP-A-8-302124 proposes a flame-retardant resin composition formed of a styrenic resin-containing thermoplastic resin composition, a phosphazene compound and a polyphenol compound; and JP-A-8-225714 discloses a thermosetting resin composition which includes a phosphazene compound. Although flame retardant properties were good, the resin compositions were not acceptable in terms of processability and appearance of molded articles produced therefrom.
Moreover, WO 03/002666 proposes a method in which a crosslinked phosphazene compound and a polyphenylene ether resin with customary molecular weight are used as a flame-retardant in a polyalkylene arylate resin. This imparted good flame retardancy to the polyalkylene arylate resin, but the resulting resin was not acceptable in terms of processability and appearance of molded articles produce therefrom.
JP-A-2001-49090 discloses a resin composition formed of a thermoplastic or thermosetting resin with a weight average molecular weight of 10,000 or more, an epoxy resin and a phosphazene compound. The resin composition uses a high-molecular weight thermoplastic or thermosetting resin, and was not acceptable in terms of processability and appearance of molded articles thereof.